It is known that a golf club comprises a head extended upward by a "hosel" or neck, to which a handle, commonly termed a shaft, is connected. For some golf clubs, especially wood-metal clubs and some irons, a filling material must be injected into the head, for several reasons.
First, the club must be precisely balanced, and the injection of material is thus performed as a final club-balancing operation. Second, for reasons of sound at impact, the interior cavity cannot remain empty.
The injection operation is generally carried out through the neck, thus requiring the operator to dismantle the shaft after verifying club adjustment, and then to remount the shaft and verify the measurement once again, while taking into account, furthermore, the weight of the glue joining the shaft to the neck. This succession of operations often entails adjustment errors.
Furthermore, the injection operation itself is performed through a single hole. The worker inspects visually the expansion of the foam in the cavity through the neck, until it reaches the desired level. A plastic plug is then inserted and fastened in place in order to halt the expansion of the foam until the latter is completely polymerized. The plug is then destroyed by machining through the neck while avoiding any removal of the filling material.
U.S. Pat. No. 4,553,755 discloses an injection procedure carried out through two orifices in the sole plate of a club, one used for the injection of the plastic material and the other for the venting of air during the operation. Once the procedure has been completed, pins are screwed in to ensure impermeability. Nevertheless, the design of this club does not avoid the restrictive visual inspection of the material level.